When considering updating a question, you should ask whether or not the update is a question in its own right. If it is, it should probably be its own question.
If the new "candidate question" is closely tied to the original question - i.e. the scope of any answers will be limited to your question, or the answer to the original question is dependent upon the answer to the new one, then it should be an edit.
In the case of the question you link, I'd say it is a valid update to the existing question. Answering this question will effectively answer your original question - it's not a separate question that is simply a small part of, for example, implementing an answer to your original question.
Effectively, your original question has changed from "how do I..." to "is this an acceptable way to..."